Typically, a wafer comprising a plurality of semiconductor dice is mounted on an adhesive tape during singulation wherein each individual die is separated while it adheres to the adhesive tape. Detaching and picking up of a die from an adhesive tape is thus an important operation in die bonding and flip chip bonding processes for assembling electronic packages.
It is a challenging task to detach a die from an adhesive tape without damaging the die when the thickness of the die is reduced to below 4 mils (about 100 microns). Dice with thicknesses of 50-100 microns have been used for mass production for some time. Mass production of dice at 30-50 microns thick is currently under preparation. Experiments for research and development in electronic packaging designs are ongoing for dice of 15-30 microns thick. Hence, an apparatus that is capable of reliably detaching very thin dice from adhesive tapes is becoming a critical machine in the realm of electronic assembly equipment.
Typically in a die bonding process, a die is detached and picked up from an adhesive tape by ejection and pick-up tools before the die is transferred to a substrate such as a lead frame, a printed wiring board (PWB) substrate or a surface of another die in stacking die applications. In a die pick-up process, a designated die on an adhesive tape is aligned with an ejection tool with push-up pins which raises the die from the underside while the adhesive tape is held down by vacuum suction. A collet or a pick-up tool is then positioned just above the top surface of the partially detached die while the die is being lifted from the adhesive tape when the push-up pins rise to an appropriate level. The collet provides vacuum suction using a vacuum generator to hold the die during the detachment process, as well as transfers the detached die from the adhesive tape to a bonding substrate.
There are various forms of die detachment and pick-up tools for facilitating detachment of a die from an adhesive tape to which it is mounted. The conventional tools include a needle-type ejector pin design, which is a traditional design for detaching a small die from an adhesive tape. FIG. 1 is an illustration of a conventional die detachment and pick-up tool 100 with needle-type ejector pins 102. The die detachment part of the tool 100 has an ejector comprising an ejector chuck 104, ejector pins 102 and an ejector cap 106. The pick-up part of the tool 100 has a collet 108 positioned above a die 110 located on an adhesive tape 112 which is in contact with an upper platform surface 107 of the ejector cap 106. Vertical movement of the ejector chuck 104 is driven by a motorised mechanism. The ejector pins 102 are positioned on top of the ejector chuck 104 and are movable with the ejector chuck 104. For small dice of dimensions such as 2×2 mm2, a single ejector pin 102 positioned at the center of the die 110 to be detached suffices to detach the die 110. Multiple ejector pins 102 are preferred for larger dice, and the ejector pins 102 are evenly distributed to achieve a uniform push-up force on the die 110 so as to reduce a pinching effect by the ejector pins 102. The ejector chuck 104 and ejector pin/pins 102 are positioned within the ejector cap 106. A vacuum channel 114 is enclosed by the ejector cap 106 in order to provide vacuum suction to the adhesive tape 112 for aiding in the delamination of the die 110 to pull the adhesive tape 112 in a direction away from the collet 108.
When the thickness of a die is reduced to less than 100 microns, the die becomes less rigid. To detach a die, peeling energy is applied to the die being detached via push-up motion of ejector pins and the vacuum suction on the adhesive tape in order to overcome a critical interfacial adhesion strength between the die and an adhesive tape. Deformation of the die may arise due to the pinching effect by the ejector pins and the bending of the die. When the applied peeling energy reaches the critical interfacial adhesion strength, the die may be detached from the adhesive tape. However, the die will crack or break when the process of deformation of the die also reaches the critical strength of the die. The critical strength of the die depends on various characteristics of the die, such as the material of the die, wafer thinning, pattern on the surface of die and sawing of the die. For conventional die pick-up using ejector pin or pins, the pinching effect and bending deformation are affected by the number, arrangement and geometry of the ejector pins. Furthermore, for a large die, the ejector pins located at the periphery of the die inhibit propagation of the detachment to the center of die. Therefore, a conventional pick-up tool using ejector pins may not be suitable for detaching a thin die from an adhesive tape.
FIG. 2 illustrates a die detachment and pick-up tool 10 which is configured for detaching a thin die 12 from an adhesive tape 18 on which the die 12 is mounted. The die 12 is supported by a plurality of vertically movable supporting plates 14 which are located within an ejector cap 16. Each plate 14 has a quadrilateral-shaped contact surface and is arranged adjacent to other similar plates 14. The plates 14 comprise a central movable supporting plate and outer movable supporting plates on opposite sides of the central movable supporting plate which together form a continuous and flat quadrilateral-shaped contact surface for supporting the die 12 on the adhesive tape 18. Each plate 14 is movable relative to the other movable supporting plates towards and away from the die 12. The tool 10 is a useful pick-up device for thin dice as it provides support and reduces the pinching effect from sharp projections pushing onto the die 12.
During the initial detachment of the die 12, maximum support provided to the die 12 avoids substantial deformation to the die 12 while it is being detached from the adhesive tape 18. A collet 20 which is connected to a bondhead is positioned above the die 12. The collet 20 contacts the die 12 and pulls the die 12 towards the collet by vacuum suction from the collet. Thus, the collet 20 holds the die 12 in place by the vacuum suction while it is being detached. After the die 12 is detached, the collet 20 is lifted completely to separate the die from the adhesive tape 18 and transports the detached die 12 away from the adhesive tape.
To achieve an optimal die detachment process and to prevent cracking the die 12, it would be desirable to provide a control system which assesses the peeling energy experienced by the die 12 by virtue of the projecting motion of the movable supporting plates 14 so that the peeling energy will not exceed the critical strength of the die 12. This is especially helpful for handling thin dice which are less rigid and therefore crack more easily.